
Numerically, we found that the fourth-order symmetry energy induces a contribution \(\lesssim 0.5\,\mathrm {MeV}\)  to the PNM EOS at densities \(\rho \approx 2\rho _0\) , see Fig. REF . For a comparison, the constraint on the PNM EOS from the chiral perturbation theory (\(\chi \mathrm {PT}\) ) [1]} is also shown. It is seen that the constructed toy model satisfies the constraint from the chiral perturbation theory.
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